The present invention relates to ink jet and like printers and, more specifically, to modifying firing signal timing therein to reduce electromagnetic interference caused by firing signal transitions.
Many types of printers are known and they include ink jet, laser and various thermal and impact printers. Ink jet printers include those that are thermally actuated (e.g., resistive element) and those that are mechanically actuated (e.g., piezo-electric element). Representative ink jet printers include those made by Hewlett Packard, Canon and Epson, etc. The electromagnetic interference (EMI) reducing techniques of the present invention are applicable to all printers and particularly to ink jet printers.
Advances in semiconductor fabrication and printhead design have led to an increase in the number of firing chambers provided on a single printhead. In a representative prior art printhead each of the plurality of firing chambers or subset thereof, may be fired simultaneously.
Increases in the number of firing chambers on each printhead lead to an increase in the resolution of a printed image and may result in improvements of both image quality and the rate at which an image (or document) is printed.
While the ability to fire multiple printheads simultaneously is advantageous in delivering ink to a desired destination (e.g., a sheet of paper), multiple simultaneous firings are disadvantageous in that they generate a significant amount of EMI due to the multiple simultaneous firing signal transitions. In other words, the firing signal for each firing chamber may change from an off state to a drive state simultaneously (i.e., large current change xcex94i in a small time change xcex94t), causing the firing signal conductors to function as de-facto antennas that radiate electromagnetic interference generated by the abrupt signal transitions. Excess EMI causes interference with or the failure of system components and impedes receiving approval from the FCC and like international agencies that set EMI emission standards.
This problem is exacerbated by continuing efforts to increase firing chamber densities. Not only do higher density circuits have more EMI generator points, but they are also more likely to be adversely affected by the deleterious effects of EMI.
Accordingly, it is an object of the present invention to provide a multiple firing chamber ink jet printhead that modifies the timing of firing signals to the firing chambers to reduce EMI.
It is another object of the present invention to provide a multiple firing chamber printhead that delays at least some the firing signals relative to one another so as to reduce the occurrence of simultaneous firing signal transitions.
It is also an object of the present invention to provide such a multiple firing chamber printhead in which the induced delays are sufficient to achieve non-simultaneous firings that reduce EMI, while not being long enough to adversely affect image quality.
It is also an object of the present invention to provide a printer that incorporates such a printhead.
These and related objects of the present invention are achieved by use of a reduced EMI printhead apparatus and method as described herein.
The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings.